bug#58288: 29.0.50; (flyspell-correct-word-before-point) followed by <down> crashes emacs

[Lars Ingebrigtsen <larsi@gnus.org>]

Andrew John De Angelis <ajd2195@columbia.edu> writes:

> - emacs -Q
> - Eval: (turn-on-flyspell)

Or `M-x flyspell-mode'.

> - write a word that's not present in the dictionary
>    (I wrote "incorrectlll")
> - place cursor at word
> - M-x flyspell-correct-word-before-point
> - press down arrow (<down>) to navigate to the 'Save word' option
> - emacs crashes
>    (in the terminal, this is the message:
>    Fatal error 11: Segmentation fault
>    zsh: abort      emacs -Q

I can reproduce this crash on Macos (but not on Ubuntu) with the current
"master".

However, I'm not well versed in debugging stuff like this on Macos, so
if somebody else could have a look, that'd be great.